Activin-class ligand (Activin (often abbreviated for specific isoforms, e.g., ActA, ActB))

Activin-class ligands are disulfide-linked dimers of inhibin β subunits, such as Activin A (InhβA/InhβA), Activin B (InhβB/InhβB), Activin C, and others. They transmit signals by binding type II serine/threonine kinase receptors (e.g., ActRIIA, ActRIIB), which then recruit type I receptors including Activin receptor-like kinases (ALK4, ALK5, ALK7). Upon receptor activation, these ligands induce SMAD2/3 phosphorylation and nuclear signaling. The specificity for receptors and antagonists varies among members: for example, ActA signals primarily via ALK4, whereas ActC and ActE signal via ALK7 and are less sensitive to inhibition by follistatin. Their physiological functions include the regulation of development, reproduction, immune responses, muscle and adipose tissue biology, and more. Pathologically, Activin-class ligands are involved in cancer, fibrosis, anemia of chronic disease, and muscular disorders. Therapeutic strategies frequently target these pathways using ligand traps, receptor antagonists, or antibody-based drugs. No major error is present in the "Activin-class ligands" designation, but structured information is best obtained at the specific ligand or receptor level (e.g., "Activin A", "Activin receptor type IIB"), since each member has unique signaling characteristics and disease associations.

Other names

ActivinsInhibin beta dimersActA (Activin A)ActB (Activin B)ActC (Activin C)ActE (Activin E)growth differentiation factor 8 (GDF8, myostatin)growth differentiation factor 11 (GDF11)

Ligand trap: drugs bind and sequester activin-class ligands or their receptors (e.g., ActRIIA/ActRIIB traps), blocking normal signaling. Inhibitor: Follistatin and its derivatives bind and antagonize activin-class ligands by preventing receptor binding. Recombinant protein therapies: engineered variants may supplement or inhibit activin signaling.